1. Field of the Invention
The present invention relates to an air conditioner operated through the years. In particular, it relates to an improvement of air conditioning ability on an air conditioner capable of conducting a natural circulation operation without using the power of a compressor. Further, the present invention relates to a method for controlling refrigerant for an air conditioner capable of conducting such natural circulation operation as well as a forced circulation operation with the power of a compressor.
2. Discussion of Background
In recent years, a technical field of removing heat from electric machines in a location represented by a computer center or a base station (hereinbelow, referred to as a shelter) accommodating relay electric devices has rapidly spread with spreading of mobile communication such as a portable telephone. Such location is required to conduct an air cooling operation throughout years. In the field of removing from the electric devices requiring an air cooling operation throughout the years, when an outdoor air temperature is low as in a winter season or a night time, it is possible to cool electronic devices by air ventilation. However, a special device for preventing fog, rain, snow, dust and so on from entering therein is necessary. Further, stable air cooling can not be performed because there is variations in an indoor air temperature depending on variations in the outdoor air temperature. Under such conditions, it is possible to use an air conditioner in which natural circulation for carrying heat by refrigerant from an indoor to an outdoor, by utilizing a temperature difference between an indoor air temperature and an outdoor air temperature and a difference of position in height between an indoor unit and an outdoor unit. In the air conditioner utilizing such natural circulation, the power of a compressor is unnecessary when operations utilizing natural circulation (hereinbelow, referred to as natural circulation operation) is to be conducted. Accordingly, it can substantially reduce an annual power consumption in comparison with an air cooling operation by using an air conditioner which conducts operations by using the compressor (hereinbelow, referred to as forced circulation operation).
Now, the operational principle of air cooling operation by the natural circulation will be described with reference to FIG. 17. FIG. 17 is a diagram showing the basic circuit for an air cooling apparatus as an air conditioner utilizing the natural circulation wherein reference numeral 2 designates a condenser, numeral 3 an outdoor fan, numeral 5 an outdoor unit, numeral 6 a liquid pipe, numeral 7 an evaporator, numeral 8 an indoor fan, numeral 9 an indoor unit located in a space to be air-conditioned and numeral 10 a gas pipe. In this case, for conducting air cooling, the evaporator 7 is provided at an indoor side and the condenser 2 is provided at an outdoor side.
The operation will be explained. When the condenser 2 is arranged at a higher position than the evaporator 7, a liquid refrigerant condensed in the condenser 2 descends by the gravity in the liquid pipe 6 to be introduced into the evaporator 7. The liquid refrigerant introduced into the evaporator 7 is vaporized by receiving a thermal load in a space to be air-conditioned, e.g., a room, and then, the vaporized refrigerant ascends in the gas pipe 10 to be returned to the condenser 2; thus, a cycle is formed.
Thus, the air cooling operation by the natural circulation utilizes a density difference between a liquid refrigerant and a gas refrigerant due to a relative position in height between the evaporator 7 and the condenser 2, as a driving force for circulating the refrigerant. The natural circulation can be realized in a case that sum of pressure losses in a refrigerant circuit comprising the condenser 2, the evaporator 7, the liquid pipe 6, the gas pipe 10 and on-off valves in the refrigerant circuit is equal to a pressure increase in the liquid pipe 6 caused by a height of liquid column.
In an air conditioner utilizing such natural circulation, an amount of refrigerant (a refrigerant quantity) to be charged has been determined from experience. Further, a state of the refrigerant has not been properly controlled in consideration of the air conditioning ability during the natural circulation operation.
Further, in an air conditioner utilizing the natural circulation, the existence of a temperature difference between an indoor air temperature and an outdoor air temperature is required. Accordingly, there is a possibility that the natural circulation operation does not function depending on environmental conditions. In this case, an air conditioner capable of effecting the forced circulation operation with use of the compressor in response to the case that the natural circulation operation does not function, is provided. In the air conditioner in combination of the natural circulation operation and the forced circulation operation, it is necessary to provide a refrigerant flow controlling means in the refrigerant circuit from the reasons that there are a variation in a refrigerant flow rate between the natural circulation operation and the forced circulation operation as well as a variation of the refrigerant flow rate due to a variation in the length of a liquid portion, a variation of the refrigerant flow rate derived from a variation of a load, and a difference of a refrigerant quantity derived from the length of the pipes extended in the circuit. In the conventional air conditioners, a reservoir provided at an outlet of the condenser or an accumulator provided at a sucking side of the compressor bore such refrigerant flow controlling function. However, the method for properly controlling a refrigerant quantity has not substantially been conducted.